use std::alloc::{alloc, dealloc, Layout};
use std::sync::atomic::{AtomicUsize};

/// 零拷贝内存管理器
pub struct ZeroCopyMemory {
    memory_blocks: Vec<MemoryBlock>,
    small_objects: ObjectPool<[u8; 64]>,
    medium_objects: ObjectPool<[u8; 256]>,
    large_objects: ObjectPool<[u8; 1024]>,
    cache_aligned: Vec<CacheAlignedBlock>,
    stats: MemoryStats,
}

/// 内存块结构
#[repr(C, align(64))]
pub struct MemoryBlock {
    data: [u8; 4096],
    used: AtomicUsize,
    next: *mut MemoryBlock,
}

// 线程安全实现
unsafe impl Send for MemoryBlock {}
unsafe impl Sync for MemoryBlock {}

/// 对象池
pub struct ObjectPool<T> {
    pool: Vec<T>,
    available: Vec<usize>,
    total_allocated: AtomicUsize,
}

/// 缓存行对齐的内存块
#[repr(C, align(64))]
pub struct CacheAlignedBlock {
    data: [u8; 64],
    metadata: CacheMetadata,
}

/// 缓存元数据
#[repr(C)]
pub struct CacheMetadata {
    access_count: AtomicUsize,
    last_access: AtomicUsize,
    flags: u8,
}

/// 内存统计
#[derive(Debug, Default, Clone)]
pub struct MemoryStats {
    pub total_allocated: usize,
    pub total_freed: usize,
    pub cache_hits: usize,
    pub cache_misses: usize,
    pub zero_copy_ops: usize,
    pub cache_line_efficiency: f64,
    pub emergency_collections: usize,
    pub usage_ratio: f64,
}

impl ZeroCopyMemory {
    pub fn new() -> Self {
        ZeroCopyMemory {
            memory_blocks: Vec::new(),
            small_objects: ObjectPool::new(),
            medium_objects: ObjectPool::new(),
            large_objects: ObjectPool::new(),
            cache_aligned: Vec::new(),
            stats: MemoryStats::default(),
        }
    }
    
    /// 零拷贝分配内存
    pub fn allocate_zero_copy(&mut self, size: usize) -> *mut u8 {
        let ptr = match size {
            0..=64 => self.small_objects.allocate(),
            65..=256 => self.medium_objects.allocate(),
            257..=1024 => self.large_objects.allocate(),
            _ => self.allocate_large(size),
        };
        
        if !ptr.is_null() {
            self.stats.zero_copy_ops += 1;
        }
        
        ptr
    }
    
    /// 零拷贝释放内存
    pub fn deallocate_zero_copy(&mut self, ptr: *mut u8, size: usize) {
        match size {
            0..=64 => self.small_objects.deallocate(ptr),
            65..=256 => self.medium_objects.deallocate(ptr),
            257..=1024 => self.large_objects.deallocate(ptr),
            _ => self.deallocate_large(ptr, size),
        }
        
        self.stats.total_freed += size;
    }
    
    /// 缓存友好的内存复制
    pub fn cache_friendly_copy(&mut self, src: *const u8, dst: *mut u8, size: usize) {
        let cache_line_size = 64;
        let mut offset = 0;
        
        while offset + cache_line_size <= size {
            unsafe {
                let src_ptr = src.add(offset);
                let dst_ptr = dst.add(offset);
                
                let src_data = std::ptr::read_unaligned(src_ptr as *const [u8; 64]);
                std::ptr::write_unaligned(dst_ptr as *mut [u8; 64], src_data);
            }
            offset += cache_line_size;
        }
        
        if offset < size {
            unsafe {
                let remaining = size - offset;
                std::ptr::copy_nonoverlapping(src.add(offset), dst.add(offset), remaining);
            }
        }
        
        self.stats.cache_line_efficiency = (offset / cache_line_size) as f64 / (size / cache_line_size).max(1) as f64;
    }
    
    /// 预取优化
    pub fn prefetch_data(&self, ptr: *const u8, size: usize) {
        let cache_line_size = 64;
        let mut offset = 0;
        
        while offset < size {
            unsafe {
                #[cfg(target_arch = "x86_64")]
                {
                    use std::arch::x86_64::_mm_prefetch;
                    _mm_prefetch(ptr.add(offset) as *const i8, 3);
                }
                
                #[cfg(target_arch = "aarch64")]
                {
                    use std::arch::aarch64::__prefetch;
                    __prefetch(ptr.add(offset) as *const i8, 0, 3, 0);
                }
            }
            offset += cache_line_size;
        }
    }
    
    /// 分配大对象内存
    fn allocate_large(&mut self, size: usize) -> *mut u8 {
        let layout = Layout::from_size_align(size, 64).unwrap();
        unsafe {
            let ptr = alloc(layout);
            if !ptr.is_null() {
                self.stats.total_allocated += size;
            }
            ptr
        }
    }
    
    /// 释放大对象内存
    fn deallocate_large(&mut self, ptr: *mut u8, size: usize) {
        if ptr.is_null() {
            return;
        }
        
        unsafe {
            let layout = Layout::from_size_align(size, 64).unwrap();
            dealloc(ptr, layout);
            self.stats.total_allocated = self.stats.total_allocated.saturating_sub(size);
        }
    }
    
    /// 获取内存统计信息
    pub fn get_stats(&self) -> &MemoryStats {
        &self.stats
    }
    
    /// 计算缓存命中率
    pub fn calculate_cache_hit_rate(&self) -> f64 {
        let total = self.stats.cache_hits + self.stats.cache_misses;
        if total == 0 { 0.0 } else {
            self.stats.cache_hits as f64 / total as f64
        }
    }
}

impl<T> ObjectPool<T> {
    fn new() -> Self {
        ObjectPool {
            pool: Vec::new(),
            available: Vec::new(),
            total_allocated: AtomicUsize::new(0),
        }
    }
    
    fn allocate(&mut self) -> *mut u8 {
        if let Some(index) = self.available.pop() {
            unsafe {
                let ptr = self.pool.as_mut_ptr().add(index) as *mut u8;
                ptr
            }
        } else {
            let mut new_obj = unsafe { std::mem::MaybeUninit::<T>::uninit().assume_init() };
            let ptr = &mut new_obj as *mut T as *mut u8;
            self.pool.push(new_obj);
            ptr
        }
    }
    
    fn deallocate(&mut self, ptr: *mut u8) {
        if !ptr.is_null() {
            let index = (ptr as usize - self.pool.as_ptr() as usize) / std::mem::size_of::<T>();
            self.available.push(index);
        }
    }
}

impl<T> Default for ObjectPool<T> {
    fn default() -> Self {
        Self::new()
    }
}

// 线程安全实现
unsafe impl<T> Send for ObjectPool<T> {}
unsafe impl<T> Sync for ObjectPool<T> {}

/// 内存访问模式优化器
pub struct AccessPatternOptimizer {
    access_history: Vec<AccessRecord>,
    cache_predictions: Vec<CachePrediction>,
}

#[derive(Debug, Clone)]
pub struct AccessRecord {
    pub address: usize,
    pub size: usize,
    pub access_type: AccessType,
    pub timestamp: u64,
}

#[derive(Debug, Clone, Copy)]
pub enum AccessType {
    Read,
    Write,
    Copy,
    Move,
}

#[derive(Debug, Clone)]
pub struct CachePrediction {
    pub address: usize,
    pub probability: f64,
    pub confidence: f64,
}

impl AccessPatternOptimizer {
    pub fn new() -> Self {
        AccessPatternOptimizer {
            access_history: Vec::with_capacity(1000),
            cache_predictions: Vec::new(),
        }
    }
    
    /// 记录内存访问模式
    pub fn record_access(&mut self, address: usize, size: usize, access_type: AccessType) {
        let record = AccessRecord {
            address,
            size,
            access_type,
            timestamp: std::time::SystemTime::now()
                .duration_since(std::time::UNIX_EPOCH)
                .unwrap()
                .as_nanos() as u64,
        };
        
        self.access_history.push(record);
        
        if self.access_history.len() > 1000 {
            self.access_history.remove(0);
        }
    }
    
    /// 预测下次访问模式
    pub fn predict_next_access(&self, current_address: usize) -> Option<CachePrediction> {
        if self.access_history.len() < 10 {
            return None;
        }
        
        let recent = &self.access_history[self.access_history.len().saturating_sub(10)..];
        
        let mut similar_patterns = Vec::new();
        for record in recent {
            let distance = (record.address as isize - current_address as isize).abs() as usize;
            if distance < 1024 {
                similar_patterns.push((record.address, distance));
            }
        }
        
        if similar_patterns.is_empty() {
            return None;
        }
        
        let avg_next = similar_patterns.iter()
            .map(|(addr, _)| *addr)
            .sum::<usize>() / similar_patterns.len();
        
        Some(CachePrediction {
            address: avg_next,
            probability: 0.7,
            confidence: similar_patterns.len() as f64 / 10.0,
        })
    }
    
    /// 优化内存布局
    pub fn optimize_layout(&mut self, addresses: &mut [usize]) {
        addresses.sort_by_key(|&addr| {
            self.access_history.iter()
                .filter(|record| record.address == addr)
                .count()
        });
    }
}